34,583 research outputs found
A simple model of price formation
A simple Ising spin model which can describe the mechanism of price formation
in financial markets is proposed. In contrast to other agent-based models, the
influence does not flow inward from the surrounding neighbors to the center
site, but spreads outward from the center to the neighbors. The model thus
describes the spread of opinions among traders. It is shown via standard Monte
Carlo simulations that very simple rules lead to dynamics that duplicate those
of asset prices.Comment: Version 2: 4 pages, 4 figures; added more stringent statistical
analysis; to appear in Int. J. Modern Physics C, Vol. 13, No. 1 (2002
The role of carbon for superconductivity in MgCNi from specific heat
The influence of carbon deficiency on superconductivity of MgCNi is
investigated by specific heat measurements in the normal and superconducting
state. In order to perform a detailed analysis of the normal state specific
heat, a computer code is developed which allows for an instantaneous estimate
of the main features of the lattice dynamics. By analyzing the evolution of the
lattice vibrations within the series and simultaneously considering the visible
mass enhancement, the loss in the electron-phonon coupling can be attributed to
significant changes of the prominent Ni vibrations. The present data well
supports the recently established picture of strong electron-phonon coupling
and ferromagnetic spin fluctuations in this compound.Comment: 4 pages, latex, corrections to the text, one reference added, one
figure correcte
Neutrino Signal of Electron-Capture Supernovae from Core Collapse to Cooling
An 8.8 solar mass electron-capture supernova (SN) was simulated in spherical
symmetry consistently from collapse through explosion to nearly complete
deleptonization of the forming neutron star. The evolution time of about 9 s is
short because of nucleon-nucleon correlations in the neutrino opacities. After
a brief phase of accretion-enhanced luminosities (~200 ms), luminosity
equipartition among all species becomes almost perfect and the spectra of
electron antineutrinos and muon/tau antineutrinos very similar. We discuss
consequences for the neutrino-driven wind as a nucleosynthesis site and for
flavor oscillations of SN neutrinos.Comment: 4 pages, 4 eps figures; published as Physical Review Letters, vol.
104, Issue 25, id. 25110
Building block libraries and structural considerations in the self-assembly of polyoxometalate and polyoxothiometalate systems
Inorganic metal-oxide clusters form a class of compounds that are unique in their topological and electronic versatility and are becoming increasingly more important in a variety of applications. Namely, Polyoxometalates (POMs) have shown an unmatched range of physical properties and the ability to form structures that can bridge several length scales. The formation of these molecular clusters is often ambiguous and is governed by self-assembly processes that limit our ability to rationally design such molecules. However, recent years have shown that by considering new building block principles the design and discovery of novel complex clusters is aiding our understanding of this process. Now with current progress in thiometalate chemistry, specifically polyoxothiometalates (POTM), the field of inorganic molecular clusters has further diversified allowing for the targeted development of molecules with specific functionality. This chapter discusses the main differences between POM and POTM systems and how this affects synthetic methodologies and reactivities. We will illustrate how careful structural considerations can lead to the generation of novel building blocks and further deepen our understanding of complex systems
Quenching of lamellar ordering in an n-alkane embedded in nanopores
We present an X-ray diffraction study of the normale alkane nonadecane
C_{19}H_{40} embedded in nanoporous Vycor glass. The confined molecular crystal
accomplishes a close-packed structure by alignment of the rod-like molecules
parallel to the pore axis while sacrificing one basic principle known from the
bulk state, i.e. the lamellar ordering of the molecules. Despite this disorder,
the phase transitions observed in the confined solid mimic the phase behavior
of the 3D unconfined crystal, though enriched by the appearance of a true
rotator phase known only from longer alkane chains.Comment: 7 pages, 3 figure
Molecular transport and flow past hard and soft surfaces: Computer simulation of model systems
The properties of polymer liquids on hard and soft substrates are
investigated by molecular dynamics simulation of a coarse-grained bead-spring
model and dynamic single-chain-in-mean-field (SCMF) simulations of a soft,
coarse-grained polymer model. Hard, corrugated substrates are modelled by an
FCC Lennard-Jones solid while polymer brushes are investigated as a
prototypical example of a soft, deformable surface. From the molecular
simulation we extract the coarse-grained parameters that characterise the
equilibrium and flow properties of the liquid in contact with the substrate:
the surface and interface tensions, and the parameters of the hydrodynamic
boundary condition. The so-determined parameters enter a continuum description
like the Stokes equation or the lubrication approximation.Comment: 41 pages, 13 figure
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